Sulphur cement generally refers to a product comprising at least sulphur, usually in an amount of at least 50 wt %, and a filler. Sulphur cement may be plasticised by the addition of a sulphur cement modifier in the sulphur cement preparation process. Such modifiers are known in the art. Examples of such modifiers are aliphatic or aromatic polysulphides or compounds that form polysulphides upon reaction with sulphur. Examples of compounds that form polysulphides are naphthalene or olefinic compounds such as dicyclopentadiene, limonene or styrene. Modifiers are usually added in an amount in the range of from 0.1 to 10 wt % based on the weight of sulphur. Usual sulphur cement fillers are particulate inorganic material with an average particle size in the range of from 0.1 μm to 0.1 mm. Examples of such sulphur cement fillers are fly ash, limestone, quartz, iron oxide, alumina, titania, graphite, gypsum, talc, mica or combinations thereof. The filler content of sulphur cement may vary widely, but is typically in the range of from 5 to 50 wt %, based on the total weight of the cement.
Sulphur cement-aggregate composites generally refer to a composite comprising both sulphur cement and aggregate. Examples of sulphur cement-aggregate composites are sulphur mortar, sulphur concrete and sulphur-extended asphalt. Mortar comprises fine aggregate, typically with particles having an average diameter between 0.1 and 5 mm, for example sand. Concrete comprises coarse aggregate, typically with particles having an average diameter between 5 and 40 mm, for example gravel or rock. Sulphur-extended asphalt is asphalt, i.e. typically aggregate with a binder that contains filler and a residual hydrocarbon fraction, wherein part of the binder has been replaced by sulphur, usually modified sulphur.
It is known to use organosilane as a stabilising agent in sulphur cement or sulphur cement-aggregate compositions to improve water stability. In U.S. Pat. No. 4,164,428 for example, a plasticized sulphur composition comprising at least 50% by weight of sulphur, a sulphur plasticizer, a finely divided particulate mineral suspending agent, and an organosilane stabilising agent is disclosed. It is mentioned that suitable organosilanes have the general molecular formula R—Si(OR′)3, wherein R′ is a low molecular weight alkyl group and R is an organic radical having at least one functional group, usually bonded to the silicon atom by a short alkyl chain. Gamma-mercaptopropyltrimethoxysilane is mentioned as a preferred organosilane.
In U.S. Pat. No. 4,376,830 a sulphur cement-aggregate composition comprising a sulphur cement and an aggregate containing an expansive clay and processes for preparing such compositions are disclosed. The processes, and resulting compositions, are characterised by the addition of certain organosilanes in the composition prior to solidifying (cooling) the composition. The resulting solidified composition has improved water stability. It is mentioned that suitable organosilanes have the formula Z—Si(R1R2R3), wherein R1, R2 and R3 may be lower alkoxy groups and Z is an organic radical attached to Si via a carbon atom and has at least one molten-sulphur reactive group. Z may for example be mercaptoalkyl. Gamma-mercaptopropyltrimethoxysilane is mentioned as a preferred organosilane.
Disadvantages of the use of gamma-mercaptopropyltrimethoxysilane are that it is very toxic and that it has a very unpleasant smell.